1. Field of the Invention
The present invention relates to a beam-forming shade for use in a vehicular headlamp, and more particularly to a beam-forming shade of the type which is disposed at a predetermined position with respect to a position of a filament (light source) so as to interrupt light emitted from the filament toward regions of a reflector of the headlamp other than a parabolic reflection surface thereof, that is, to mainly direct the light from the filament only toward the parabolic reflection surface region of the reflector, thereby effectively distributing the light reflected by the reflector.
2. Related Art
Various kinds of shades have been known as disclosed in U.S. Pat. Nos. 4,268,895, 4,344,119 and 4,321,658. One conventional shade of the type as shown in FIG. 1 comprises a cylindrical shade body 2 and a frame-shaped connecting member 4 having a pair of mounting parts which are welded together to form an integral construction. Thin metal plates 3 and 5 for forming the cylindrical shade body 2 and the frame-shaped connecting member 4, respectively, are obtained in a developed form by cutting, as shown in FIGS. 2A and 2B, and then they are bent into respective predetermined shapes, and then are integrally welded together. The shade 2 thus assembled is connected to a reflector 6 by a pair of screws 8 through the pair of mounting parts. A bulb 1 is fitted to a rear apex portion of the reflector 6.
In the conventional shade described above, however, a residual thermal strain may exist in the welded portion since the shade body 2 and connecting member 4 are formed by welding into the integral construction. Thermal stresses, due to a difference between the temperature when the bulb is lit and when it is off, would repeatedly act on the welded portion, and also stresses due to vibrations repeatedly act on the welded portion, which suffers from a problem that the welded portion between the shade body and the connecting member may be subjected to fatigue failure. On the other hand, the welding step is indispensable to the manufacture of the shade and, therefore, time required for assembling the same must correspondingly be increased, thus arising another problem of increased cost. There is a further problem that because of the necessity of the welding operation applied to the portion between the shade body and the connecting member, defective products are produced at a considerable rate, thus worsening the yield. Moreover, as shown in FIG. 1, since the conventional shade 2 is provided with a bridge-like frame bridging toward the two mounting parts, the shade suffer from a difficulty that some parts of light beam reflected by the reflector 6 are obstructed by the bridge-like frame thereby influencing the required light beam distribution. Moreover, since the conventional shade 2 is provided with a pair of mounting parts, it requires two screws 8 for actually connecting to the reflector, which increases the manufacturing cost.